In oil reservoir development, a drillstring is used to drill a borehole (well). The term “drillstring” refers to the combination of the drillpipe, the bottomhole assembly and any other tools used to make the drill bit turn at the bottom of the wellbore. During the drilling, the neutral point of the drillstring needs to be considered for various reasons, such as stress reduction and management. A neutral point is the point at which the drillstring moves from a state of compression stress to a state of tension stress. Components of the drillstring below the neutral point are in compression stress such that they need to have high bending stiffness to avoid, for example, buckling. In addition, if there is a jarring device in the drillstring, the jarring device needs to be positioned either below or above the neutral point depending on the type of the jarring device (i.e., compression or tension) such that, for example, accidental jar firing can be avoided.
Conventionally, the neutral point is determined and considered in bottomhole assembly (BHA) design in the well plan stage. A BHA refers to the lower portion of a drillstring, including, if any, from the bottom up in a vertical well, the bit, bit sub, a mud motor (in certain cases), stabilizers, drill collars, heavy-weight drillpipe, jarring devices (“jars”) and crossovers for various threadforms. The neutral point is calculated using a torque and drag engine. Conventionally, the inputs to a torque and drag engine include the designed BHA, wellbore geometry, survey (e.g., the type of wellbore) and the estimations/simulations of various factors related to the drilling process. However, the estimation/simulation may deviate from the situations in the actual drilling. As such, in the drilling, the actual neutral point may be different than the pre-calculated neutral point. In addition, in the actual drilling process, the neutral point may move due to, e.g., changes in the values of the torque and drag factors, and other relevant factors.